Small wireless antennas eliminate wiring between chips
Within MIANT (Monolithic integrated antennas), scientists utilised parts of the circuits to significantly reduce overall antenna size and proposed ways to overcome interference issues between circuit components. In particular, the team proposed using the circuit ground planes as radiating elements for the integrated antennas. To achieve this, they cut the circuitry ground supply plane into patches and used them as antenna electrodes. This allows for optimal usage of chip area as the antennas share the same metallisation structure with the circuits. The circuit ground plane is manufactured in the top metallisation layer of the complementary metal-oxide semiconductor (CMOS) process. The team combined numerical and experimental techniques to address some key issues that pose a barrier to successful antenna integration. The silicon substrate of the embedded antennas presents high dielectric losses in the microwave range. A high-resistivity substrate helped minimise the dielectric losses in the substrate. In addition, scientists used very thin substrates to reduce the volume where losses occur. Results demonstrated that antenna integration into very thin substrates enables high wireless chip-to-chip data rates that can reach up to 10 Gbps. Another strand of work was dedicated to producing an experimental set-up to investigate interference issues between the integrated digital circuits and the wireless chip-to-chip link. The set-up consists of an on-chip slot antenna built in the CMOS ground supply plane and digital circuitry under the antenna. When the digital circuit operates, the transistor sends out switching noise at the antenna port. Nevertheless, this noise was found to be lower than the thermal noise when the antenna operates at 24 GHz and the switched signal has a frequency of 25 MHz. A new extrapolation formula estimates the frequency at which the switching noise becomes lower than the thermal noise. Except for digital systems, this study into integrated antennas has wide implications for sensors for efficient data harvesting.
Keywords
Wireless, antennas, circuits, MIANT, integrated antennas, ground planes, chip-to-chip
